Atomistic Studies of Deformation Mechanism of Nanocrystalline Al-Ti and Al-Fe Alloys from First-Principles

Abstract:

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We investigated the contribution to the high yield strength due to the solid solution
strengthening in nanocrystalline Al-Ti alloys produced by a vapor quench method. The misfit strain
due to solute Ti atom in aluminum was obtained from the first principles calculation. Then, the
theoretical result of the contribution to the yield strength due to the solid solution strengthening was
estimated from the misfit strain using the Friedel’s theory. In dilute Al-Ti alloy, the theoretical
results of the solid solution strengthening from the misfit strain was in good agreement with the
analytical result using the measured grain size and yield stress.

Abstract: Recently nanocrystalline Al-Fe alloys produced by a vapor quench method have been reported. These alloys are supersaturated solid solution and exhibit high strength with good ductility. It is postulated that the high strength of the Al-Fe alloys could be achieved by both the nano-grained structures and the solid solution strengthening. The contribution to the yield strength due to both the grain size strengthening and the solid solution strengthening were analyzed from the experimental data. Then the contribution to the yield strength due to the solid solution strengthening was estimated from the misfit strain calculated from the first principles in order to compare with analytical results estimated from the experimental data.

Abstract: The aim of this paper is to study the effect of relaxing the assumption in the Peierls
analysis that the dislocation must be wide compared to the atom spacing. To do this the use of the
continuum description of the in-plane strains caused by the presence of an edge dislocation is
replaced by an atomistic interaction taken to be linear elastic. It is found that in this case the inplane
interactions give a contribution to the overall misfit energy changes that are not present in the
Peierls analysis because of the use of a continuum approach. This contribution modifies these
energy changes so that the total misfit energy is a minimum at the conventional low energy
positions (whereas in the Peierls analysis it is a maximum) and gives values of the Peierls stress in
reasonable agreement with those measured.

Abstract: Strengths of multilayered structures have been investigated using three-dimensional
discrete dislocation dynamics (DDD) simulation. The multilayered structure was modeled as a stack
of misfit dislocation networks which must exist at an interface between adjoining crystals having
different lattice constants. Passages of a single mobile dislocation through several kinds of network
stacks were simulated. The critical stress required for the dislocation passage depended on the
dislocation spacing of the network, the number of network sheet and the spacing between network
sheets.

Abstract: Dislocation configurations in two single-crystal superalloys during high-temperature low-stress creep (1100°C, 137 MP) were illustrated schematically with the use of transmission electron microscope (TEM). For an alloy with a small lattice misfit, the dislocations move in the combination of climbing and gliding processes. In the primary stage, the dislocations first move by slip in the g-matrix channels. When they reach the g¢ cuboids, they move by climb along the g¢ cuboid surfaces. In the secondary creep stage, dislocation reorientation in the (001) interfacial planes happens slowly, deviating from the deposition orientation of <110> to the misfit orientation of <100>. For an alloy with a large lattice misfit, the dislocations are able to move smoothly by cross slip in the horizontal g channels. The dislocation reorientation from the deposition orientation of <110> to the misfit orientation of <100> in the (001) interfacial planes can be completed in the primary creep stage.

Abstract: Experimental studies proved that structures and properties of misfit dislocations and their intersections (nodes) in semi-coherent interfaces strongly affect thermal and mechanical stability of interface. Employing atomistic simulations, we reveal that misfit dislocation lines can exhibit a spiral pattern (SP) or remain straight in association with dislocation character at nodes. By analyzing nodes formation processes in terms of kinetics and energetics, we found that the variation is ascribed to the competition between core energy of misfit dislocation and interface stacking fault energy with respect to coherent interface.